The microstructure and surface hardness of Ti6Al4V alloy implanted with nitrogen ions at an elevated temperature

Abstract

The effect of an elevated temperature during nitrogen ion implantation on the microstructure and on the surface hardness of Ti6Al4V titanium alloy was examined. The implantation process was carried out at fluences of 1⋅1017, 2.7⋅1017 and 6⋅1017cm−2 and at ion energy 90keV. The implanted samples were annealed at 500°C during the implantation process. X-ray diffraction analysis was performed to obtain a phase characterization and a phase quantification in the implanted sample surface. The surface hardness was investigated by nanoindentation testing, and the nitrogen depth distribution was measured by Rutherford Backscattering Spectroscopy. Elevated temperature led to increased formation of a TiN compound. It was found that a mixture of TiN and an α-Ti(+N) solid solution had a predominant amount of TiN for samples with fluence of 2.7⋅1017cm−2 or higher. Elevated temperature during ion implantation caused an increase in surface hardening more towards the depth of the substrate in comparison with room temperature implantation. The hardness showed a remarkably significant increase at a fluence of 1⋅1017 and 2.7⋅1017cm−2 compared to samples implanted at the same fluences and at room temperature. There is a discussion of such mechanisms that explain the observed hardening more towards the depth of the substrate, and the increase in hardness.